The invention relates to a ship screw, pump screw or turbine screw for use under water, comprising a front side and a rear side, wherein water or another liquid is forced from the front side to the rear side in use, and comprising a hub and at least two blades extending from said hub.
Such screws are generally known. It is a known fact that screws are one of the causes of fish mortality. Furthermore, such screws produce a lot of noise caused by turbulence. In the processing of blood by means of a blood pump, for example, cavitation may be a problem.